Diabetes is a major risk factor for stroke. Clinical evidence indicates that diabetes accelerates development of atherosclerosis, but mechanisms that account for this interaction are not clear. The investigators speculate that hypercholesterolemia may exaggerate endothelial dysfunction through increased superoxide in vessels during hyperglycemia. The goal of this project is to examine pathophysiological interactions between hyperglycemia and hypercholesterolemia in carotid and intracranial cerebral arteries. It is likely that hyperglycemia will accelerate development of atherosclerosis in the carotid artery, but because diabetes is also a disease of small vessels, it will be particularly important to examine effects in the cerebral microcirculation. There are 3 major aims. First, studies are proposed to test the hypothesis that hypercholesterolemia augments generation of superoxide and endothelial dysfunction in carotid and cerebral arteries during hyperglycemia. Second, studies are planned to identify the contribution of endothelium, vascular muscle, and adventitia to superoxide in carotid and cerebral arteries during hyperglycemia and hypercholesterolemia. Third, studies are proposed to elucidate enzymatic mechanisms that account for cerebral vascular dysfunction. The investigators propose to test the hypothesis that vascular NADPH oxidase contributes to increased levels of superoxide and, therefore, vascular dysfunction during diabetes and hypercholesterolemia. Studies are planned in carotid and basilar artery of rabbits and mice in vitro, and in carotid artery and cerebral vessels in vivo. Endothelial vasomotor function will be examined, and superoxide in vessels will be studied with lucigenin chemiluminescence, and with laser confocal microscopy. Levels of superoxide dismutase (SOD) and superoxide in the vessel wall will be altered by pharmacological approaches, adenoviral mediated gene transfer of CuZnSOD to different layers of the vessel wall, with a newly made CuZnSOD transgenic mouse targeted to vascular smooth muscle, and with mice lacking functional NADPH oxidase. These studies may provide important insight about mechanisms which produce accelerated cerebral vascular dysfunction during diabetes and hypercholesterolemia.